Increasing demands for improved quality control and efficiency in production of steel and other metals requires that weight of input components and products be accurately measured at various steps in production of steel or other metal products. Although input metals and compounds for a melt (also called a heat) are typically weighed before or during placement directly into a furnace, or into a ladle used for melting steel or other metals in a furnace, burn-off or out-gassing of materials contained in a melt, or removal of slag, during melting and mixing, can change weight of a melt or heat during processing. This alteration of components of the melt may in turn adversely affect properties or quality of the finished metal. Thus, it is important to be able to obtain an accurate weight of a ladle of molten metal after removal from a furnace and before additional processing of the metal.
In many cases, after processing in a furnace, a ladle of molten metal is removed from the furnace by a crane and placed on a transfer car to be moved to a separate portion of a steel mill or other metal processing facility for additional processing. A transfer car is a generally self-propelled vehicle that rides on steel wheels on rails somewhat like a railroad car. A transfer car may have a simple flat platform somewhat like a flatbed rail car, onto which a ladle of molten metal or components for a melt may be placed, or a transfer car may contain a structure somewhat like that of a short steel bridge with receptacles that accept support members extending near a top of a ladle and suspends a ladle for transport. Ladles may be placed upon or removed from transfer cars by overhead cranes or other equipment capable of handling the weight of a ladle of molten metal. A full ladle of molten steel may weigh as much as 500,000 pounds or more, whereas an empty ladle may weigh approximately 150,000 pounds.
Temperatures of components on a transfer car located near a ladle of molten steel can easily exceed 600 degrees Fahrenheit. Past practice has been to attempt to measure weight of a ladle of molten steel based on deformation of structure of a transfer car as indicated by relative movement of cantilevered rods connected to different points on structural members of the transfer car or as measured by strain gages attached directly to these structural members. Other practices make use of load cell pins located at structural joints that directly support weight of a ladle or that support weight of a transfer car platform and a ladle. However, cantilevered rods, load cell pins, and other elements of existing measurement systems, as well as movable joints between supported elements and underlying support structures, are exposed to falling debris or even splashed with molten metal, and are also exposed to severe temperature and shock and vibration environments, with a result that existing methods and apparatus for measuring weight of ladles of molten metal require frequent recalibration and have proven generally unreliable and costly to use.
It is thus one object of the instant invention to provide more durable load cells and associated structural and electrical elements that may be mounted in a relatively protected location on a transfer car. It is another object of the invention to provide a load cell that can provide more accurate and reliable indications of weight changes associated with placement of ladles on a transfer car than hithertofore possible. It is yet another object of the invention to provide a load cell requiring less maintenance and cleaning of transfer car or other vehicle structure. It is yet another object of the invention to provide a load cell and weighing system requiring less frequent calibration to maintain accurate weight measurement capabilities. It is a further object of the instant invention to provide a heat-resistant load cell to permit reliable operation at temperatures of 550 degrees Fahrenheit or more associated with proximity to a ladle of molten metal. Other objects of the invention will become apparent upon a reading of the following specification.